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Novak Mavar K.,INA Industry of Oil Plc.
Rudarsko Geolosko Naftni Zbornik | Year: 2017

Migration risk assessment of the injected CO2 is one of the first and indispensable steps in determining locations for the implementation of projects for carbon dioxide permanent disposal in depleted hydrocarbon reservoirs. Within the phase of potential storage characterization and assessment, it is necessary to conduct a quantitative risk assessment, based on dynamic reservoir models that predict the behaviour of the injected CO2, which requires good knowledge of the reservoir conditions. A preliminary risk assessment proposed in this paper can be used to identify risks of CO2 leakage from the injection zone and through wells by quantifying hazard probability (likelihood) and severity, in order to establish a risk-mitigation plan and to engage prevention programs. Here, the proposed risk assessment for the injection well is based on a quantitative risk matrix. The proposed assessment for the injection zone is based on methodology used to determine a reservoir probability in exploration and development of oil and gas (Probability of Success, abbr. POS), and modified by taking into account hazards that may lead to CO2 leakage through the cap rock in the atmosphere or groundwater. Such an assessment can eliminate locations that do not meet the basic criteria in regard to short-term and long-term safety and the integrity of the site. © The Author(s).


Indicator based geostatistical methods (Indicator Kriging and Sequential Indicator Simulations) are the mostly used methods for facies mapping or modelling. Although it is assumed that in facies variables should be discrete, it is possible to apply these methods on continuous variables as well. If a variable is continuous, a cumulative probability distribution function has to be created. Methodology includes a series of cut-offs. On the cumulative probability distribution function, probabilities for all cut-o s can be defined. Based on cut-offs, all the data can be divided into two groups: (1) the data which has values lower than the cut-o and (2) the data which has values higher or equal than the cut-offs. In this way, the indicator variable takes a value of 1 at all locations where the value is higher or equal than the cut-o and 0 otherwise. The larger number of cut-o s, the more precise the cumulative distribution function is. Indicator Kriging maps show the probability of certain lithofacies appearing in some location. On the other hand, stochastical realizations provide a different number of solutions for the same input data set. Those solutions can be very similar, but never identical. It is important to emphasize that all obtained solutions are equally probable. Results of Sequential Indicator Simulations are also probability maps. There are several advantages for Indicator based methods. They do not ask for a normal distributed input dataset (e.g., can be implemented for bimodal distribution), and show connectivity of the largest or smallest values. Indicator Kriging and Sequential Indicator Simulations are applied for porosity mapping of the Upper Miocene sandstone reservoir in the Sava Depression. During the Upper Miocene, sands were deposited through turbiditic currents in the deepest part of the sedimentation area, forming turbiditic channels. Such channels can be recognized on the probability map for the cut-o 19 % in Indicator Kriging as well as in Sequential Indicator Simulation maps. © 2017, Eaton Publishing Company. All rights reserved.


Novak K.,INA Industry of Oil Plc. | Malvic T.,INA Industry of Oil Plc.
Environmental Earth Sciences | Year: 2013

Enhanced oil recovery based on CO2 injection is expected to increase recovery from Croatian oil fields. Large quantities of CO2 are generated during hydrocarbon processing produced from gas and gas condensate fields situated in the north-western part of Croatia. First CO2 injection project will be implemented on the Ivanić Oil Field. Numerical modelling based on Upper Miocene sandstone core samples testing results have shown the decrease of oil viscosity during CO2 injection. Some of the characteristics of the testing samples are porosity 21. 5-23. 6 %, permeability 14-80 × 10-15 m2 and initial water saturation 28-38. 5 %. Water alternating foam (WAF) and water alternating gas (WAG) simulations have provided satisfactory results. The WAF injection process has provided better results, but due to the process sensitivity and costs WAG is recommended for future application. During the pilot project 16 × 106 m3 CO2 and 5 × 104 m3 of water were injected. Additional amounts of hydrocarbons (4,440 m3 of oil and 2. 26 × 106 m3 of gas) were produced which confirmed injection of CO2 as a successful tertiary oil recovery mechanism in Upper Miocene sandstone reservoirs in the Croatian part of the Pannonian Basin System. © 2012 Springer-Verlag.


Novak K.,INA Industry of Oil Plc. | Malvic T.,INA Industry of Oil Plc. | Malvic T.,University of Zagreb | Velic J.,University of Zagreb | Simon K.,University of Zagreb
Environmental Earth Sciences | Year: 2014

During 2003-2006, a pilot project of alternating water and CO2 injection was performed on a limited part of the Upper Miocene sandstone oil reservoir of the Ivanić Field. During the test period oil and gas recovery was significantly increased. Additionally 4,440 m3 of oil and 2.26 × 106 m3 of gas were produced. It has initiated further modelling of sandstone reservoirs in the Ivanić Field in order to calculate volumes available for CO2 injection for the purpose of increasing hydrocarbon production from depleted sandstone reservoirs in the entire Croatian part of the Pannonian Basin System. In the first phase, modelling was based on results of laboratory testing on the core samples. It considered applying analogies with world-known projects of CO2 subsurface storage and its usage to enhance hydrocarbon production. In the second phase, reservoir variables were analysed by variograms and subsequently mapped in order to reach lithological heterogeneities and to determine reliable average values of reservoir volumes. Data on porosity, depth and reservoir thickness for the "Gamma 3" and the "Gamma 4" reservoirs, are mapped by the ordinary kriging technique. Calculated volume of CO2 expressed at standard condition which can be injected in the main reservoirs of the Ivanić Field at near miscible conditions is above 15.5 billion m3. © 2013 Springer-Verlag Berlin Heidelberg.


Tomislav M.,University of Zagreb | Ana M.B.,INA Industry of Oil Plc.
Geologica Carpathica | Year: 2012

The Croatian part of the Pannonian Basin System includes several Miocene chronostratigraphic (sub)stages mostly characterized by weak permeable clastic sediments. They are often also mature source rocks at depths of more than 2500 m, from Late Badenian to Early Pannonian ages, represented by marls and calcitic marls, and kerogene Types II and III. The other types of weakly permeable sediments are tight sandstone mostly of Badenian age. Those two lithotypes are potential unconventional reservoirs described in the Bjelovar Subdepression, regarding their age, geological evolution, lithology, porosity and permeability. Domination of kerogene Type III and low total organic carbon defined marls as gas-bearing source rocks. Both marls and tight sandstones mostly have porosity less than 10 % and permeability less than 10-3 μm2. It is about 10-100 times lesser permeability than in conventional reservoirs. Weakly permeable zones are highly stochastically distributed and fluid flows are relatively short (several meters), which could be enhanced only by the using hydraulic or other fracturing techniques.


Malvic T.,INA Industry of Oil Plc. | Malvic T.,University of Zagreb | Jovic G.,INA Industry of Oil Plc.
Journal of Maps | Year: 2012

The Kloštar Oil Field is situated at the north-western part of Sava Depression in the Croatian part of the Pannonian Basin. It is a typical geological structure that evolved through the Neogene and Quaternary and that is why the structural evolution is reconstructed using palinspastic mapping (i.e., using selected chronostratigraphic horizons as datum planes). The total map set includes six structural and 15 palaeostructural maps interpolated over five Elog markers and one border. The mapping has been performed using the Ordinary Kriging. The maps were used for the interpretation of geological evolution during the Neogene and Quaternary, and particularly a description of hydrocarbon reservoir formation and migration pathways. The structural development can be explained through two phases of transtension and two of transpression that existed regionally in the Sava Depression. However, the maps and cross-sections that are described locally show changes of dominant tectonic styles, particularly during the Quaternary when most of the field was a depositional centre. © 2012 Journal of Maps.


Malvic T.,INA Industry of Oil Plc | Malvic T.,University of Zagreb | Velic J.,University of Zagreb
Petroleum Geoscience | Year: 2010

The Molve Field is the most important gas-condensate reservoir in Croatia. This petroleum system is not typical for the Pannonian System, because it comprises several reservoir lithologies, relatively high structural closure and significant tectonic influence on the field's compartmentalization. Strike-slip extension in the Middle Miocene and younger Late Miocene and Pliocene tectonics formed the present-day tectonic setting. Reservoir stratigraphy includes four lithofacies (from Devonian to Neogene) with a unique gas-water contact. The lithologies encompass cataclased granite, gneiss, schists, quartzites, dolomites, limestones and grainstones. Source rocks were generated in lacustrine organic facies and migration occurred in the Late Miocene to Pliocene. Reservoir gas includes 4.5-15.7% C2+, but also non-hydrocarbon components. Analysed porosity data were approximated with a normal-distribution curve in lithofacies I, II and III, making it possible to calculate mean and variance easily by descriptive statistics. Moreover, gas production and effective thicknesses generally can be linked through a linear trend. However, significant deviations in the expected increased production rate with regard to greater reservoir thickness are observed for particular wells. This is a result of locally abrupt changes in effective porosities and permeabilities, and the size of the drainage area along the main fault zones. These faults resulted in significant compartmentalization of the field. Furthermore, owing to significant facies variations, permeability and porosity gradually change, especially in the vertical direction. Significant reserves of condensate (3 106 m3) and gas (43 500 106 m3) with a high recovery rate of 71% make this field significant for geological reservoir models. The well-established geological model for this field and its stable high pressure have maintained production rates at a present level of approximately 2900 m3 gas and 165 m3 condensate per day, thus providing a valuable example for other large heterogeneous reservoirs in the Pannonian Basin. © 2010 EAGE/Geological Society of London.


Zelenika K.N.,INA Industry of Oil Plc. | Malvic T.,INA Industry of Oil Plc.
IAMG 2010 Budapest - 14th Annual Conference of the International Association for Mathematical Geosciences | Year: 2010

Located 35 km east of the Croatian capitol Zagreb, in the Sava depression, the Kloštar oil field covers an area of some 30 km2. Its hydrocarbon reservoirs were discovered in Palaeozoic igneous rocks and Miocene sediments. These reservoirs are subdivided into a number of operational units called 'reservoir series', among which the most important are fine- to medium-grained Early Pontian sandstones, called '1st sandstone series' that contain most of the oil reserves. Thickness of this reservoir was analysed using geostatistical simulation method called Sequential Indicator Simulations (abbr. SIS). The input dataset consisting of 19 hard data (wells) with average reservoir thicknesses ranging from 1 to 25m was used for making histogram in Excel™ and six thickness classes were defined with width of 4m. However, histogram analysis on such a small data set is not reliable and transformation had to be done using programs Surfer 8.0™ (licensed) and Grid Histogram™ (freeware). Original dataset had been interpolated by Inverse Distance Weighting method, obtaining grid with 7900 values, as base for new histogram calculation, confirming previously defined six cut-offs (5, 9, 13, 17, 21 and 25 m) and constructing cumulative density function (CDF). Omnidirectional indicator semivariograms were calculated for each cut-off and approximated (using Variowin 2.21™) with standardized theoretical models with sill=1 and nugget=0.6. It means that 3rd order stationarity is assumed, accepting only the intrinsic hypothesis as the minimum for dataset (mean is independent and semivariograms exist). SIS realizations were based on Simple Kriging techniques. Final model contained 630010 cells in each of 100 realizations created for thickness. Results show that variations in thickness are approximately isotropically dispersed. Thickness mostly varies between 10 and 25 meters. It indicates on approximately similar depositional condition in the largest part of the mapped reservoir, with larger thicknesses observed along "stripes" oriented NW-SE or NNW-SSE.


Ivanisevic D.,Croatian Geological Survey | Malvic T.,INA Industry of Oil Plc. | Malvic T.,University of Zagreb
Journal of Maps | Year: 2015

The Pannonian Basin System (PBS) and associated parts of the surrounding orogens (SOs) were selected for a regional geochemical mapping of concentrations of potentially toxic metals, with the sample media the topsoil horizon. Geochemical data form a sample space that is different from Euclidean, and therefore standard statistical methods are not applicable for such data. To apply standard statistical methods, data were transformed to Euclidean space by using a special case of an isometric log-ratio transformation for a composition consisting of two parts (the first part is the metal concentration of interest; the second part is the total concentration of all other elements in the composition). Estimations were performed using deterministic (Ordinary Kriging) and stochastic (sequential Gaussian simulations (SGS)) methods. The resulting maps provide insight into the distribution of certain metals in the PBS and associated parts of the SOs, and are intended to serve as base maps for further studies. The maps obtained with SGS provide additional information on the variability (uncertainty) of estimation. © 2015 Danijel Ivanišević


Balic D.,INA Industry of Oil Plc | Malvic T.,INA Industry of Oil Plc
Geological Quarterly | Year: 2013

The Adriatic Sea is an epicontinental, closed sea, part of the Mediterranean. It formed in the Late Miocene, and ended structurally during the Pliocene and Quaternary, when most of its sediments were deposited. The larger Pliocene and Quaternary depressions occur mostly by the western coast, where the deposits are several thousand metres thick, and were sourced from the Alps and the Apennines. The east coast is characterized by the large and elongated Dinarides Mts., that have continental drainage extremely close to the shoreline and a very small erosional rate. Consequently, eastern inflows were and are very short, including strongly tidal estuaries that erode only small volumes of mostly carbonate detritus, adjacent to frontal islands or mountains, with restricted depositional areas. The Neretva River deposits make up part of the largest contemporary delta system on the eastern Adriatic coast, and have been analysed in this study using three seismic sections and one exploration borehole. These deposits are recognized inside the Neretva and Korcula channels, assuming that processes operating during Quaternary glacial phases shifted the delta tens of kilometres to the west in the past on several occasions.

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